BACKGROUND: Hippocampal sclerosis (HpScl) in the elderly is often associated with neurodegeneration.METHODS: We studied the clinical and pathologic features of HpScl in 205 consecutive patients with dementia who came to autopsy from 1997 to 2008, focusing on associations with TAR DNA-binding protein 43 (TDP-43) pathology and allelic variants in the progranulin (GRN) and apolipoprotein E (APOE).RESULTS: Of the 205 dementia patients, 28 had HpScl (14%). TDP-43 pathology was more frequent in cases with HpScl compared with those without HpScl (89% vs. 24%). GRN rs5848 T-allele but not APOE ε4 was associated with HpScl. In cases of HpScl with TDP-43 pathology and age of onset after 75 years (n=11), 8 had Alzheimer disease (AD)-like amnestic syndrome, but most (6 of 8) had pathology not consistent with AD (Braak stage III or less), including 4 with frontotemporal lobar degeneration with TDP, 1 with diffuse Lewy body disease, and 1 with "pure HpScl."CONCLUSIONS: HpScl is common in an elderly cohort with dementia, occurring in 14% of the cases in this series, and 89% have TDP-43 pathology, often associated with a risk variant in GRN. Patients with HpScl who present after the age of 75 years often have presentations consistent with AD, but at autopsy have non-Alzheimer pathologies. Elderly patients with HpScl may be mistaken for AD.